Physics: Post your doubts here!

[Oliveme]

Hi please help me solve this, 71. answer is B but how can it be 20 J? I tried 8=4+Fs but it doesn't work

The change in energy is 4 joules (as 8 -4). So the change in kinetic energy will be twice = 4 x 2 = 16 joules.
But remember this is the change, not the final energy. So the 4 joules will become 16 + 4 = 20 joules.
Hope this was helpful. Sorry about the delayed reply.

 

[TaffsAsLevel]

The change in energy is 4 joules (as 8 -4). So the change in kinetic energy will be twice = 4 x 2 = 16 joules.
But remember this is the change, not the final energy. So the 4 joules will become 16 + 4 = 20 joules.
Hope this was helpful. Sorry about the delayed reply.

Basically difference is 16 J but initial is 4 J making it 20 J , thanksss =D

 

[biba]

doing past papers for p5.. is that all for preparation ?

 

[hassanhijazi1995]

Hi everyone, AsSalamoAlaikum Wr Wb...

To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

So post your PHYSICS doubts in this thread. InshaAllah other people here will help me and you all.

NOTE: If any doubts in the pastpapers, please post the link! You can find links here!

Any Physics related notes and links will be added here in this post. Feel free to provide the links to your notes around the forum, or any other websites!
Thanks!
Jazak Allah Khair!

Physics Notes:

Some links & Notes - by destined007

As physics p1 MCQS YEARLY Solved [explaination]
Physics Practical Tips - by arlery

Notes for A2 Direct Sensing (Applications) - shared by sweetiepie

Physics Summarised Notes (Click to download)

AS and A-Level Physics Definitions

A2: Physics Revision notes - by smzimran

Paper:5 Finding uncerainty in log - by XPFMember

Physics Paper 5 tips - by arlery

Physics Compiled Pastpapers: <Credits to CaptainDanger for sharing this..>

Here are the compiled A level topical Physics questions in PDF form...

Paper 1 : http://www.mediafire.com/?tocg6ha6ihkwd

Paper 2 & Paper 4 : http://www.mediafire.com/?g65j51stacmy33c

(Source : http://www.alevelforum.com/viewtopic.php?f=15&t=14)

hey there how r u

do u know how to calculate the uncertinities in second question for p 5 ??

 

[Soldier313]

doing past papers for p5.. is that all for preparation ?

yep i guess that's it

 

[kalpaveen]

can anyone explain to me how to draw ERROR BARS....plz....

 

[Omar99]

please help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w09_qp_11.pdf
question no. 6, 9,15,25,33
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_12.pdf
question no. 9, 25, 26 and 27

 

[Omar99]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w11_qp_11.pdf
question no. 2, 18, 23, 24, 29, 32, 37
please help some one......

 

[Oliveme]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_11.pdf
question no. 2, 18, 23, 24, 29, 32, 37
please help some one......

2) Here we use the formula K.E. = 1/2 mv^2
Now we know the mass but we do not know the velocity. But they've given us the distance. So using the distance, we find speed. 100 m can be covered in about 10 seconds by an athlete (this is more of using your common sense here.) So speed becomes = 100/10 = 10 ms^-2
K.E. = 1/2 x 80 kg x 10^2 = 4 x 10^3 joules. So answer is B.

29) For stationary waves in pipes, the formula is ----> fn = (2n - 1)c / 4L where L = length of pipe, fn = frequency, c = speed of the waves (3 x 10^8)
For pipe P, the length is 35 cm which means 1 and 3/4 of a stationary wave can form, since the wavelength is 20 cm.
For pipe Q, the length is 50 cm, which means 2 and 1/2 stationary waves can form.
So, in both pipes stationary waves can form, answer is A.
Remember, at nodes you have no vibration of air molecules but at anti-nodes, there is maximum vibration of air molecules.


32) The arrows point downwards which means the charge at the top is positive and the bottom is negative. So, the +Q will be attracted downwards and the -Q will be attracted upwards, spinning the rod anti-clockwise. The resultant force is zero because F = E/Q and the Q (both charges) are equal but opposite. So resultant force is zero. If the charges weren't the same in magnitude, then we would have a resultant force.

37) The circuit B is just wrong because ammeters are never connected in parallel to the components you're trying to get a reading of, they're always in series.
Circuit C won't show the largest reading because currents get divided in parallel circuit so that some goes in one branch and some in the other branch. And so the ammeter will show only part of the current reading.
Circuit A and D are now left. In circuit D, the resistors are in parallel but the ammeter is in series with the power supply and so, you see when the current divides, each branch of the current only has to go through one resistor and so not much energy in electrons is lost. but in A, the current passes through two resistors and more work is done by the electrons in passing through two resistors. Answer is D.

please help in http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w09_qp_11.pdf
question no. 6, 9,15,25,33

15) M1V1 = M2V2 ----> 2 kg x 2 ms^-1 = 1 kg x V2
V2 = 2 x 2/ 1
= 4 ms^-1 so the velocity of 1 kg trolley is 4 ms^-1
Kinetic energy of M1 trolley = 0.5 x 2 x 2^2 = 4 joules
Kinetic energy of M2 trolley = 0.5 x 1 x 4^2 = 8 joules
Total kinetic energy = 4 + 8 = 12 joules
Since all the stored potential energy is converted to kinetic (assuming no heat losses) --> gain in K.E. = loss in P.E
So energy stored is 12 joules. (D)

 

[shreeya95]

need help here http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s07_qp_5.pdf Q.No.2(a)....after we convert the equation into R=(Pl^2/V) + Ro ( P= rho) what do we write as conclusion???

 

[anishniroula]

Can anyone please help me out in Q2.c.iii ?
I have found the gradient, which is 0.56. But I am having difficulties in finding the errors of the gradient.
The absolute errors that I've got on the table are: 0.13, 0.08, 0.06, 0.04, 0.04 and 0.03.
Please help me how to find the gradient errors!!!

And also Q2d!!!

PLEASE!

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20(9702)/9702_s07_qp_5.pdf

to calculate the error in gradient firstly calculate the gradient of worst fit line and subtract the gradient if worst fit line and the gradient of best fit line.
to calculate the value of rho in qno 2 d firstly re arrange the equation to R/L^2=rho/V+Ro. where Ro is constant. R/L^2 is gradient so put the value of gradient and value of volume given to calculate rho.
to calculate uncertainity in this use the gradient of worst fit to do the same above and subtract the values.
Hoped it helped..

 

[anishniroula]

need help here http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s07_qp_5.pdf Q.No.2(a)....after we convert the equation into R=(Pl^2/V) + Ro ( P= rho) what do we write as conclusion???

I think after writing this eqn we should say that that are directly propotional and if one changes it affects to another..

 

[Ahmad Zaeem]

Please can anyone post a picture of the diagram of M/J 2012 P5 Q1......

 

[TaffsAsLevel]

The change in energy is 4 joules (as 8 -4). So the change in kinetic energy will be twice = 4 x 2 = 16 joules.
But remember this is the change, not the final energy. So the 4 joules will become 16 + 4 = 20 joules.
Hope this was helpful. Sorry about the delayed reply.

Hey hey can you help me again, this time it's paper 5 june 2007 , if for example l is a quantity in cm with an uncertainty +- 0.4, so what happen to the uncertainty if they ask for l^2

 

[bomberblitz]

13)
View attachment 27641

22) Volume = mass/density = 3.5 x 10^-25 kg / 9.2 x 10^3 kg m^-3
= 3.36 x 10^-10 m^3
So, answer is C.

Q13--shouldn't the force acting on the box viewed as a horizontal force force to the left? the pulley converts the weight of the mass to that force.
Anyhow I don't get (8-6)x9.81 as 8.0 is the mass in kg's, 6.0 is the frictional force in units N. Can u plz explain it a bit

 

[shreeya95]

I think after writing this eqn we should say that that are directly propotional and if one changes it affects to another..

mark scheme says that This mark is not scored for Rbeing proportional to l^2. so how do we write the conclusion that confirms the relationship between R and l??

 

[Oliveme]

Hey hey can you help me again, this time it's paper 5 june 2007 , if for example l is a quantity in cm with an uncertainty +- 0.4, so what happen to the uncertainty if they ask for l^2

Let's assume l is 10.2 (+- 0.4). When l is squared, we square the two extreme points and subtract them to get uncertainty in the l squared value.
10.2^2 = 104.04 and uncertainty = (10.2+0.4)^2 - (10.2-0.4)^2
= 10.6^2 - 9.8^2
= 112.36 - 96.04 = 16.32
So, we have 104.04 (+- 16.32).
Hope you get it.

 

[Oliveme]

Anyhow I don't get (8-6)x9.81 as 8.0 is the mass in kg's, 6.0 is the frictional force in units N. Can u plz explain it a bit

We subtract the two to get the resultant force. Frictional force opposes the driving force and so the total force becomes 2N.

 

[TaffsAsLevel]

Let's assume l is 10.2 (+- 0.4). When l is squared, we square the two extreme points and subtract them to get uncertainty in the l squared value.
10.2^2 = 104.04 and uncertainty = (10.2+0.4)^2 - (10.2-0.4)^2
= 10.6^2 - 9.8^2
= 112.36 - 96.04 = 16.32
So, we have 104.04 (+- 16.32).
Hope you get it.

Daaayyyuumm thanksss a ton you know everything

 

[kiara15]

can any1 guide me how to calculate absolute errors in gradient and y intercept? alsoow to how to draw worst fit line in graph? plzz